In sawmills, logs are cut into slab sided articles of wood in the process of converting the logs into useable lumber. For this purpose, the log is fed into a device referred to as a chipper or canter (hereinafter “chipper/canter”). The chipper/canter has a rotating cutting head incorporating a plurality of cutting members, typically removable knives, saws, or combinations thereof. The cutting head is variously referred to as a chipper head, canter head, slabbing head, or conical head. The term “chipper” refers to one function of the chipper/canter, i.e., to produce chips that are used to form other wood products, such as pulp, paper, and particle board. The term “canter” refers to another function of the chipper/canter, i.e., to cut a piece from the log, referred to as a “cant,” having at least two parallel, substantially flat or slab sides, and the term “slabbing” refers to producing one or more of these sides. All of these heads are termed “conical” heads due to their geometry; the cutting surface defined by rotation of the head is actually frustoconical in shape.
The cutting head rotates about its axis of symmetry and the log is translated toward the head in a direction that is aligned with the longitudinal axis of the log and perpendicular to the axis of rotation of the head, causing the log to interfere with the cutting surface of the head and thereby cutting the log to produce elongate, slab sided articles of wood, and chips.
There are typically two opposed cutting heads operating on the log at substantially the same time to produce, during one pass of the log, two sided cants, and often there are four cutting heads for producing four sided cants from the log in a single cutting operation.
As the cutting surface defined by the rotating conical cutting head is actually frustoconical, it includes a flat annular portion as well as a conical portion that flares outwardly from the annular portion. The plane of the annular portion of this cutting surface is in the plane of the slab sides of the articles of wood and produces a finish on these sides. However, the log first encounters the conical portion of the cutting surface of the rotating cutting head, which cuts and tears chips from the log in preparation for the finishing provided by the annular portion as translation of the log in the direction just indicated is continued.
The annular portion of the cutting surface defined by the rotating conical cutting head is typically produced either by a plurality of circumferentially spaced knives, or a disk-saw. Any such structure is referred to hereinafter as a “facing” portion of the cutting head because it produces a “facing” cut on the log that defines the slab sides of the lumber.
The conical portion of the cutting surface is typically produced by a plurality of staggered knives that are often arranged in spaced apart circular patterns, or alternatively in a spiral pattern, so as to trace a frustoconical surface as the head rotates. Any such structure is referred to hereinafter as a “chipping” portion of the cutting head because it cuts chips from the log.
It will be appreciated that a significant volume of the log must be removed as chips because the log is roughly circular and the lumber produced therefrom is rectilinear. So the chips are a waste product of the conversion of the log to lumber, but they are at the same time useful as constituents of manufactured wood products. They are particularly useful where their dimensions are controlled, and a dimensional parameter of the chip that is particularly important to control is the chip length.
The knives of the chipping portion are attached to a body of the head either directly or through intermediate members, and the body of the head may or may not itself be essentially frustoconical in shape. The body is often referred to in the art as “solid.”
FIG. 1 shows schematically a log 2 being processed, i.e., cut, chipped, or sawn into lumber by a pair of opposed chipper/canter cutting heads rotating about an axis of rotation “L.” Each cutting head includes chipping knives having cutting edges that define a chip cutting surface indicated as 3, and facing knives, or alternatively saw teeth, having cutting edges that define a face cutting surface indicated as 4. The cutting heads establish a depth of cut “d” between the slab sided faces “f” of the cut lumber, the location being indicated with a reference line “REF,” and the original, curved outer surface “s” of the log.
To adjust the depth of cut, the heads are moved in and out, i.e., axially, in the direction of the arrows, in the direction of the axis of rotation L.
FIG. 2 shows a prior art cutting head 5 in isometric view, and FIG. 3 shows the same head looking down the axis “L,” in the plane of head rotation. The conical chip cutting surface is 6 and the annular facing surface is 7. The chip cutting surface is defined by chipping knives 8, namely 8a and 8b, having cutting edges 9. The knives 8 are separated by an angular distance θ, and the head rotates at an angular velocity ω. Also shown is the log 2 about to be fed into the cutting head at a feed speed “v.”
The chip length is the distance the log travels in the time that the head turns sufficiently to move a knife (e.g., 8b) into the same position that a preceding knife (e.g., 8a) was in. Thus the chip length is equal to v·θ/ω.
A “limiter” structure 10 is typically provided between adjacent knives 8. The limiter has an outer surface (hereinafter “limiting surface”) 10a that limits radial movement of the log, holding the log in place, to prevent or at least minimize surging and bucking. The limiting surface is, overall, at a somewhat lower radial elevation “r” than that of the adjacent knives, and in addition its radial elevation smoothly curvilinearly decreases over the angular distance between the adjacent knives from its elevation proximate the first knife to contact the wood, e.g., the knife 8a, to the next knife, e.g., the knife 8b. This change in radial elevation of the limiter surface is best seen in FIG. 4 (compare the radial elevations “r1” and “r2”) showing the limiter surface by itself.
The amount of overall elevation drop, or “relief,” provided for the limiting surfaces relative to the knife cutting edges is dictated by the same parameters that determine chip length. Therefore, adjusting the chip length requires changing this elevation. More particularly, decreasing the chip length, e.g., by decreasing the log feed speed or by increasing the angular velocity of the cutting head, requires increasing the radial elevation of the limiting surfaces, to move the limiting surfaces closer to the elevation of the cutting edges of the chipping knives.
The shape of the curve defining how the elevation of the limiting surfaces drops in-between adjacent knives is also dictated by the same parameters that determine chip length.
The limiter 10 as shown in FIGS. 2-4 is formed in a continuous ring which is not typical, though it best illustrates the aforementioned elevation variation. However, typically, the limiting surface is provided as discrete, modular limiter elements that are individually mounted between the associated chipping knives. In that case, adjustments require dismounting, repositioning or replacing, and finally re-mounting the limiter elements. As there are typically a number of the limiter elements, this is a time consuming procedure. While the continuous ring eliminates the need to individually adjust or replace a number of limiter elements to adjust chip length, the adjustment requires replacing the ring. Since there may be a number of different chip length adjustments required, this exacts a penalty in the cost and inconvenience of obtaining, storing, and maintaining a number of different rings.
Accordingly, an improved chipper/canter head of modular design according to the present invention provides for quicker and easier adjustment of chip length, as well as other advantages.